This invention relates generally to a development apparatus used in ionographic or electrophotographic imaging and printing apparatuses and machines, and more particularly is directed to donor rolls for a development system.
One common element utilized in machinery is a roll. The roll typically includes a body and two journals or stems which extend outwardly from opposed ends of the body. Bearings, either in the form of journals or rolling element bearings, permit the rotatable mounting of the rolls onto a frame of the machinery. The bearings are typically mounted to the outer periphery of the journals of the roll. These rolls, particularly those for use in precision equipment, may be expensive and difficult to manufacture. One particular type of machinery that utilizes rolls to a great extent is that of a printing machine. In a printing machine, a substrate typically in the form of a paper roll or cut paper sheets are fed through various steps in the printing process. The substrate is guided along a paper path by rolls and processing steps are often applied to the substrate through the use of rolls.
Generally, the process of electrophotographic printing includes charging a photoconductive member to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive surface is exposed to a light image from either a scanning laser beam or light flashed upon an original document being reproduced. This records an electrostatic latent image on the photoconductive surface. After the electrostatic latent image is recorded on the photoconductive surface, the latent image is developed.
Two component and single component developer materials are commonly used for development. A typical two component developer comprises magnetic carrier granules having toner particles adhering triboelectrically thereto. A single component developer material typically comprises toner particles. Toner particles are attracted to the latent image forming a toner powder image on the photoconductive surface, the toner powder image is subsequently transferred to a copy sheet, and finally, the toner powder image is heated to permanently fuse it to the copy sheet in image configuration.
The electrophotographic marking process given above can be modified to produce color images. One color electrophotographic marking process, called image-on-image processing, superimposes toner powder images of different color toners onto the photoreceptor prior to the transfer of the composite toner powder image onto the substrate. While the image on image process is beneficial, it has several problems. For example, when recharging the photoreceptor in preparation for creating another color toner powder image, it is important to level the voltages between the previously toned and the untoned areas of the photoreceptor. Moreover, the viability of printing system concepts such as image-on-image processing usually requires development systems that do not scavenge or interact with a previously developed image. Several known development systems, such as conventional magnetic brush development and jumping single component development, are interactive with the image bearing member, making them unsuitable for use with image-on-image processes.
One particular version of a scavengeless development system uses a plurality of electrode wires closely spaced from a toned donor roll. The donor roll is loaded with toner using conventional two component magnetic brush development. An AC voltage is applied to the wires to generate a toner cloud in the development zone. The electrostatic fields from the latent image attract toner from the toner cloud to develop the latent image.
Since hybrid scavengeless development relies on a continuous, steady toner powder cloud at the nip between the latent image and the donor roller, the speeds at which the rollers operate are significantly higher and the accuracy requirements are much more precise.
The purpose and function of scavengeless development are described more fully in, for example, U.S. Pat. No. 4,868,600 to Hays et al., U.S. Pat. No. 4,984,019 to Folkins, U.S. Pat. No. 5,010,367 to Hays, or U.S. Pat. No. 5,063,875 to Folkins et al, these references are totally incorporated herein by reference.
For proper operation of a donor roll in a hybrid scavengeless development, the diameter tolerance, runout and surface finish requirements of the donor roll are very critical and require very precise dimensions.
Furthermore, donor rolls typically have a long length and a small diameter. For example, donor rolls may have a length of, for example, 18 to 24 inches and a diameter from 1 to 1xc2xd inches.
Precision rolls, whether for use as a donor roll or for another purpose, are typically made by machining a body from a solid cylindrical stock. To provide for journals at opposing ends of the rolls, typically a hole or counterbore is machined in each of the opposed faces of the cylindrical body. Journals are machined from smaller cylindrical stock and are cut to length and fitted into the counterbored apertures in the opposed ends of the cylindrical body.
The processes of counterboring a solid body, of machining cylindrical journals and of inserting the cylindrical journals into the body have several major disadvantages, particularly when used to manufacture a large quantity of high-quality, precision rolls.
Precision rolls, such as those for a donor roll, require a outer periphery that has precision size, roundness and runout requirements with respect to the journals to which bearings are mounted to provide for rotation of the roll. As the roll is rotated about the journals of the roll, the outer periphery of the roll may have an eccentric pattern or runout with respect to the mounting journals. For the proper operation of a donor roll, the runout requirements may be as precise as to be within 0.000,025 meters (25 microns). Obtaining such a low runout is very difficult when utilizing the process steps of counterboring of the body and inserting journals in the counterbores.
Runout measured between the solid body periphery and the counterbore inside diameter must be added to the roundness measured of the solid body as well as to the roundness measured of the journals to accumulate the runout of the assembled roll.
Donor rolls in hybrid scavengeless development systems require certain semiconductive electrical properties for the proper formation of the toner cloud required to develop the latent image. Such semiconductive electrical properties are obtained either through the use of an anodized coating over an aluminum donor roll or by the use of a ceramic coating placed over an aluminum donor roll. A more complete description of the ceramic coating for a donor roll is described more fully for example in U.S. Pat. No. 5,473,418 to Kazakos et al.
The use of a ceramic coating greatly compounds the difficulty in providing an accurate precision donor roll. The application of a ceramic coating to an aluminum donor roll is very expensive in that the ceramic material itself is somewhat expensive and in the fact that the coating process for applying a coating of ceramic to a donor roll is very expensive. A typical process for the application of the ceramic is a thermal spray process. Such thermal spray processes include for example a plasma spray. A thermal spray process causes oxides to form in the ceramic layer.
The oxides form in a somewhat unpredictable manner. Oxides in the ceramic coating result in porosity within the ceramic layer. The oxides produced through the thermal spray process cause porosity in the ceramic layer. This porosity creates problems in obtaining the required surface finish for proper operation of a ceramic roll. Further, the porosity in the surface may lead to arcing between the wires in the donor roll.
The oxides formed in the thermal spray process of the ceramic coating determine or assist in determining the electrical properties, namely the time constant, of the donor roll. Inconsistencies within a donor roll and from donor roll based upon the problems in obtaining consistent oxides through the thermal spray process may cause variations and inconsistencies in the types and quantity of oxides formed in the ceramic process thereby causing variations in the time constant or electrical properties of the donor roll.
Because the thermal spray process is inaccurate and expensive, the outer periphery of the donor roll must be machined after the thermal spraying process. Since the thermal spraying process is so time consuming and expensive and since the thickness of the layer of around 180 microns must be maintained at a minimum level, the donor roll periphery must be very accurately machined both prior to the thermal spraying operation as well as after the thermal spraying operation. Thus two very slow time consuming expensive grinding operations, namely grinding operations before and after the thermal spraying process, must be performed. These added precision grinding operations increase the cost and difficulty in obtaining a quality donor roll.
Attempts to reduce the runout from this process include subsequent machining or grinding of the outer periphery of the body while rotating the body about the assembled journals. This additional machine step adds cost to the manufacturing of the donor rolls.
In addition to the increased difficulty in obtaining a precision roll from the prior art process of an assembled roll, the use of an assembled roll is very expensive. For example, not only must a solid cylindrical body be manufactured but the journals must be separately manufactured. Further, the counterbores on the ends of the solid body must be machined. Further, the journals must be accurately machined to fit the bores on the solid body. Also the journals must be assembled into the bores by the use of an appropriate technique, such as press fitting or shrink fitting the journals within the bores.
In addition to the cost and difficulty in manufacturing such an assembled roll, the use of an assembled roll can cause quality problems in that if the press fit process or the shrink fit process is not properly performed, the solid body may become loose from the journals requiring the replacement of the roll.
The machining processes to prepare the journals, the solid body and the assembled donor roll require that the components and assemblies be located in difficult manners during the machining steps. The relocations or transfers of the locating points of the different parts and assemblies of the donor roll lower the quality in the form of roundness concentricities, coating thickness uniformity, and cylindricity of the donor roll complicating the difficulty in obtaining a quality donor roll.
The roll of the present invention is intended to alleviate at least some of the above-mentioned problems.
The following disclosures may be relevant to various aspects of the present invention:
The relevant portions of the foregoing disclosures may be briefly summarized as follows:
U.S. Pat. No. 5,585,909 discloses a heating device, which can be used in the fixing unit of an image forming apparatus, such as an electrophotographic copying or printing machine, for fixing a toner image on a final substrate. The heating device which is in the form of a heated fuser roller is provided with bands or coatings of material which impede the transfer of heat from the fuser roller to bearing structure associated therewith. The bands or coatings are applied by plasma spraying a ceramic material on either the surface of a fuser roll core or on journals of end caps, depending upon the specific construction of the fuser roller.
U.S. Pat. No. 5,473,418 discloses a donor roll having a ceramic coating for use with an electrode structure in a scavangeless development unit of an electrostatographic printer. The ceramic coating consists essentially of a suitable mixture of alumina and titania by weight giving the donor roll a desired resistivity.
U.S. Pat. No. 5,194,050 discloses a positioning device for preventing an endless belt passed over a plurality support rollers from being shifted to either of opposite sides in the axial direction of the rollers. A pair of forcing elements are located at both ends of at least one of the support rollers for forcing back, when the belt is shifted toward either of opposite ends of the support roller to contact the end of the latter, the belt toward the center of the roller in the axial direction of the roller. The forcing elements each are implemented as a plurality of spaced flanges. The maximum diameter of the flanges sequentially increases from the innermost flange to the outermost flange in the axial direction of the roller. The plurality of flanges may be replaced with a single spiral flange.
U.S. Pat. No. 5,168,841 discloses a tappet for an internal combustion engine comprises a tappet main body and a ceramic seat plate. The tappet main body is constituted by axially separated first and second parts which are made of different metallic materials. The first part is for installation in a hole of a cylinder block for sliding therein. The second part is for installation between a push rod and a cam. The metallic material for the second part is more wear-resistant than that of the first part. The ceramic seat plate is brazed to the second part, and the first and second parts are joined together by welding such as electron beam welding, laser beam welding, etc.
U.S. Pat. No. 5,144,885 discloses a ceramic-metal friction welded member includes a ceramic member formed with an annular notch in an outer circumference of its surface and a metal member joined onto the annular notch of the ceramic member by friction welding. A ceramic cast-in bonded piston includes a crown made of a ceramic material having an annular notch formed in an outer circumference of its surface, a metal annular member joined onto the annular notch of the crown by friction welding, and a piston main body made of an aluminum alloy surrounding the crown by cast-in bonding. A ceramic cast-in bonded piston includes a crown made of a ceramic material, a piston main body made of an aluminum alloy surrounding the crown by cast-in bonding, and an annular member made of a metal different from aluminum and joined by friction welding to an outer circumference of a surface of the crown in contact with the piston main body.
U.S. Pat. No. 5,129,784 discloses in a ceramic rotor and metal shaft assembly, a ceramic rotor which has a protruded portion and is joined at the protruded portion to a recessed portion of a metal shaft by shrinkage fit or the like fitting method of fixedly holding the protruded and recessed portions relative to each other by making the mating circumferential surfaces of the protruded and recessed portions pressed against each other. The recessed portion has a minimum thickness wall between a circumferential wall and a bottom wall. The protruded and recessed portions have a set relationship of 0.05 less than /=t/d less than /=0.2 where t is a thickness of the minimum wall portion of the recessed portion and D is an outer diameter of the protruded portion.
U.S. Pat. No. 5,063,875 discloses an apparatus which develops an electrostatic latent image. A transport roll advances developer material from a chamber to a donor roll. The donor roll advances the toner particles to the latent image. The latent image attracts toner particles from the donor roll. In order to improve the speed with which toner particles removed from the donor roll are replaced, an alternating voltage is applied between the two rolls. The magnetic transport roll is driven to rotate at a surface velocity at least 2, but not more than 5 times that of the rotational surface velocity of the donor roll. Also, the compression pile height (CPH) vs. the spacing between the spacing between the donor roll and the transport roller (DRS) is found to be optimal when meeting the ratio CPH:DRS=2:3.
U.S. Pat. No. 5,010,367 discloses a scavengeless/non-interactive development system for use in highlight color imaging. To control the developability of lines and the degree of interaction between the toner and receiver, the combination of an AC voltage on a developer donor roll with an AC voltage between toner cloud forming wires and donor roll enables efficient detachment of toner from the donor to form a toner cloud and position one end of the cloud in close proximity to the image receiver for optimum development of lines and solid areas without scavenging a previously toned image.
U.S. Pat. No. 4,984,019 discloses an apparatus in which an contaminants are removed from an electrode positioned between a donor roller and a photoconductive surface. A magnetic roller is adapted to transport developer material to the donor roller. The electrode is vibrated to remove contaminants therefrom.
U.S. Pat. No. 4,962,002 discloses ceramic-metal composite bodies and a process for the production thereof. The ceramic-metal composite body includes a metallic member and a ceramic member which are integrally joined together by fitting a projection formed on the ceramic member to a recess formed in the metallic member. The projection of the ceramic member is fitted and joined into the recess of the metallic member in a vessel of which the inside is kept at an atmosphere having a pressure lower than an atmospheric pressure. The pressure of air remaining in a space left between the recess and the fitted projection is lower than that of the air in the space when the projection is fitted into the recess in the atmospheric pressure. An apparatus for fitting and joining the projection of the ceramic member to the recess of the metallic member is also disclosed, which includes a pressure-reducible vessel which is provided with a space for receiving at least the projection of the ceramic member and the recess of the metallic member, a sealing structure including O-rings or the like, a pipe opening for exhausting air inside the vessel, and a movable push rod for pressing and fitting the projection of the ceramic member into the recess of the metallic member.
U.S. Pat. No. 4,874,674 discloses a metal-ceramic composite body which is produced by fitting a protruding portion of a ceramic member into a concave portion of an intermediate member and joining the intermediate member to a metallic member. In this case, a difference between the inner diameter in the concave portion of the intermediate member and the outer diameter in the protruding portion of the ceramic member is not less than 0.2% of the outer diameter in the protruding portion when the protruding portion is pulled out from the concave portion.
U.S. Pat. No. 4,868,600 discloses a scavengeless development system in which toner detachment from a donor and the concomitant generation of a controlled powder cloud is obtained by AC electric fields supplied by self-spaced electrode structures positioned within the development nip. The electrode structure is placed in close proximity to the toned donor within the gap between the toned donor and image receiver, self-spacing being effected via the toner on the donor. Such spacing enables the creation of relatively large electrostatic fields without risk of air breakdown.
U.S. Pat. No. 4,864,343 discloses a pressure roll is disclosed particularly for fixing and developing sheet material which is treated by passing through a high pressure nip defined by a pair of the rolls. The roll includes a support shaft and a cylindrical roll body secured to the shaft. To produce a uniform force along the pressure nip when a pair of the rolls are placed under load, the body is formed from a body material having a modulus of elasticity which varies as a function of position along the length of the body. The body is encased in a cylindrical shell.
U.S. Pat. No. 4,806,160 discloses a metallizing composition comprising an oxynitride glass of the Mgxe2x80x94Alxe2x80x94Si system and/or the Yxe2x80x94Alxe2x80x94Si system and a powder of a high-melting-point metal. This composition has a good affinity with a nitride ceramic material and a carbide ceramic material and is useful for forming metallized layers on substrates of these ceramic materials.
U.S. Pat. No. 4,776,070 discloses a roller which has a roller body having a small electrical resistivity, a bonding layer formed substantially uniformly on the outer peripheral surface of the roller body, a lower insulating layer provided on the bonding layer; a heat generating layer provided on the lower insulating layer and a ceramic matrix and a metallic resistance layer, constituted by a metal dispersed in the ceramic matrix. The metallic resistance layer extends substantially continuously in the lengthwise direction of the roller, a heat generating layer. The roller has an upper insulating layer provided on the heat generating layer, a protective layer formed on the upper insulating layer so as to prevent offset of the toner images, an electrode layer formed on each end of the roller and adapted to connect the heat generating layer to an external power source; and side protective layers covering at least the side surface of the heat generating layer, and the side surfaces and the axially outside surfaces of the lower insulating layer.
U.S. Pat. No. 4,468,299 discloses a nonconsumable electrode assembly suitable for use in the production of metal by electrolytic reduction of a metal compound dissolved in a molten salt, the assembly comprising a metal conductor and a ceramic electrode body connected by a friction weld between a portion of the body having a level of free metal or metal alloy sufficient to effect such a friction weld and a portion of the metal conductor.
The Welding Handbook, Volume 2, Welding Processes, describes solid state welding and friction welding in particular.
In accordance with one aspect of the present invention, there is provided a roller. The roller includes a ceramic body, an aluminum member attached to the ceramic body, and a shaft attached to said aluminum member.
In accordance with another aspect of the present invention, there is provided a development roller for use in a machine in which marking particles are advanced toward a latent image to form a developed image. The development roller includes a body, a member frictionally welded to the body, and a shaft attached to the member.
In accordance with a further aspect of the present invention, there is provided a development unit for use in a printing machine in which marking particles are advanced toward a latent image to form a developed image. The development unit includes a housing defining a chamber therein for storing a supply of marking particles therein. The housing defines an aperture therein and a development roller. The roller is rotatably mounted to the housing and positioned adjacent the aperture. The development roller is adapted to advance the marking particles from the chamber toward the latent image. The development roller includes a body, a member frictionally welded to said body, and a shaft attached to said member.
In accordance with yet another aspect of the present invention, there is provided an electrophotographic printing machine of the type in which marking particles are advanced toward a latent image to form a developed image. The printing machine includes a development unit. The development unit includes a housing defining a chamber therein for storing a supply of marking particles therein. The housing defines an aperture therein and a development roller. The roller is rotatably mounted to the housing and positioned adjacent the aperture. The development roller is adapted to advance the marking particles from the chamber toward the latent image. The development roller includes a body, a member frictionally welded to the body, and a shaft attached to the member.
In accordance with still another aspect of the present invention, there is provided a process for manufacturing a development roller for use in a machine in which marking particles are advanced toward a latent image to form a developed image. The process includes the steps of providing a body, frictionally welding a member to the body, and attaching a shaft to the member.